As you can see I'm not afraid to show my ignorance, but I'd never heard of one until I got on this board.
TIA

 

It's the piece beihind your throttle body (with the pony on it) that allows air to flow into the intake manifold.

 

its the upper half of your intake manifold,,,

 

technically, a plenum is a distribution box in a air movement system where there is one entrance for air entering the box and multiple exits for air leaving the box. the first portion of the upper intake on a fuel injected 5.0 engine is the plenum portion of the intake. on a carb system, the plenum is the box area directly below the carburetor mounting flange.

 

^^^^^^ Could have not put it better!!!!! [sm=smiley32.gif] Good technical answer I like it, But now a question for ya, If that is the case then the plenum on my 01 is not what i purchesed for C&L because it only has one entrance and one exit for the air? I am not trying to argue am just wondering if it has to have multiple exits for the air, to be a plenum?

 

some people call the plenum the entire intake air system from the throttle blades to the area where the individual intake runners diverge into the various intake ports, so I guess they can call it a plenum if they want to.
on a 5.0 engine, the EGR spacer is technically a part of the plenum area, but you don't ever hear anyone refer to it that way.
and when you add a spacer under a carb, you are increasing the volume of the plenum too which tricks the engine into thinking the intake is bigger than it really is and this shifts the peak power point upward in the rpm range.

 

Thanks roundman for clairfing that for me!! [&:]